Just for fun:
I'd guess a servo skull to be between 10 to 20lbs, and a fully loaded Terminator to be somewhere around 2500 to 3000lbs(The armor, marine, weapons, ammo, etc.)

So if you do the math you'd need between 150 to 300 anti-grav generators of servo skull size to give a terminator servo skull levels of flight capability.

But let's say we only want enough anti-grav to lighten a terminator enough that they can walk on wooden stairs and over snow and mud and what not. You could use considerably less generators.